In ordinary speech, "coherence" means the quality of hanging together and making sense. The word "interference" implies getting in the way, causing trouble. Physics, however, gives those terms new meaning. Waves are coherent if they line up in phase, as do the photons coming out of a laser or the quantum wavefunctions of electrons in a superconductor. Interference can be constructive or destructive, depending on whether the waves reinforce or cancel one another out. So although "constructive interference" sounds like an oxymoron ("sharp dull") it really expresses a logical and important concept --- especially if one wants to focus energy in a precise pattern. Perhaps metaphorical figures of speech do something analogous for ideas?